RDS Bugfix - Replica creation with Allocated Storage and IOPS

[corentone]

Ignore allocated storage while creating a Read Replica

• Closes Issue Creating very large database causes Error: error modifying DB Instance (orders-replica-7-p): InvalidParameterCombination: You must specify both the storage size and iops when modifying the storage size or iops on a DB instance that has iops. #12493

Tests:

• The acceptance test (allocatedStorageAndIops that would be previously failing), shows the bug by
  setting up a Replica DB with both IOPS and Allocated storage.
• Also Added an acceptance test for Iops modification to confirm code is ok because of the returned error
  message in the issue. Didn't show failures previously.

Fix:

• Ignore allocated storage when creating a read replica as this value cannot be different from the primary.
• Update doc to reflect param handling difference.

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Closes Issue #12493

Release note for CHANGELOG:

Ignore allocated_storage in RDS DB Instance creation if `replicate_source_db` is set.

Output from acceptance testing:

❯ make testacc TEST=./aws TESTARGS='-run=TestAccAWSDBInstance_ReplicateSourceDb_AllocatedStorageAndIops'; say done
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -count 1 -parallel 20 -run=TestAccAWSDBInstance_ReplicateSourceDb_AllocatedStorageAndIops -timeout 120m
=== RUN   TestAccAWSDBInstance_ReplicateSourceDb_AllocatedStorageAndIops
=== PAUSE TestAccAWSDBInstance_ReplicateSourceDb_AllocatedStorageAndIops
=== CONT  TestAccAWSDBInstance_ReplicateSourceDb_AllocatedStorageAndIops
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_AllocatedStorageAndIops (1874.12s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	1876.199s

[corentone]

@bflad You seem to be the main person contributing to the rds resources, Im curious if you have any comment on how to make it better to get it fixed :)

[corentone]

Up. It's been in the queue for a long time and I'd love to work with someone to get it in.
@anGie44 maybe would you have some time?

[YakDriver]

Looks good 🎉

Output from acceptance tests (us-west-2):

--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_AllocatedStorageAndIops (1735.36s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_Iops (1898.43s)

Output from acceptance tests (GovCloud):

--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_AllocatedStorageAndIops (1714.20s)
--- PASS: TestAccAWSDBInstance_ReplicateSourceDb_Iops (1870.51s)

[corentone]

Thanks @YakDriver for driving it through the finish line!

[github-actions]

This functionality has been released in v3.50.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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